There are numerous systems for the presentation of electronic imagery to viewers. The simplest use projectors for multiple viewers designed to project an image on a viewing surface, such as a screen. Common examples are film or movie projectors and slide or transparency projectors. Other systems are limited to single viewers. For example, head-mounted displays using special glasses allow viewers to move their head while images are optically superimposed on real scenes. More immersive systems entirely obscure a viewer's field of view and replace it with a synthetic view. These systems typically utilize a computer-controlled projector to present the imagery through a suitable optical system. The computer can also provide an interactive experience through the use of image processing and viewer feedback devices.
Immersive systems can be either portable or fixed. Portable systems typically utilize glasses or visors that obscure any sight of the real world and project a synthetic image either into the viewer's eyes or onto a personal screen seen only by the viewer. Fixed systems are generally placed within a special environment with appropriate fixtures and a screen onto which is projected the synthetic image. Viewers enter the environment to view the imagery. Training systems such as flight simulators typically use this approach. Alternatively, fixed systems can project images directly into a viewer's eyes (rather than onto a screen) while the viewer is seated in a fixed position. U.S. Ser. No. 09/738,747 filed Dec. 15, 2000 entitled A Monocentric Autostereoscopic Optical Apparatus and Method, describes such a system.
Systems that project images into a viewer's eyes, in particular stereoscopic viewing systems, require careful alignment of the image projectors with the viewer's eyes. This is problematic, since viewers are of different sizes and frequently move their head in a multiplicity of directions: forward and backward, up and down, left and right, and rotationally around any of three axes. With head-mounted systems this problem is obviated by fixing the projector's position with respect to the eyes (for example with glasses).
Systems that project images directly into a viewer's eyes but are not mounted on the viewer's head must compensate for the relative position and movement of the viewer's eyes with respect to the image projector to ensure that the image is projected into the viewer's eyes. This can be done by tracking the position of the viewer's eyes. Such eye-tracking systems are well known and very sophisticated. For example, EP 0 350 957 A3 entitled Image Pickup Apparatus and Eye Tracking Method Using the Same describes such a system. Compensation for the relative motion of the viewer's head and the image projected by the projection apparatus is then calculated with a computer and the components within the projector are moved to re-align the image with the viewer's eyes. However, the range and type of motion accommodated by the projection system can be very restricted, typically to compensate for a lateral movement of the head from left to right or vice versa. This restricts the viewer's natural body movement and leads to fatigue while viewing. Moreover, viewers of different size cannot be readily or comfortably accommodated.
There is a need, therefore, for an improved system to compensate for viewer movement in a system that projects images into a viewer's eyes so as to align a projected image with a viewer's eyes.